The basal diet of most of the cattle and buffaloes in Vietnam
is based on agro-industrial residues, roadside grass or grazing
on boundaries between crops. These diets are imbalanced in
nutritional value and variable according to seasons.

In order to develop a sustainable ruminant production system
in Vietnam, efforts are directed to making the best use of local
feed resources by adjusting the production system according to
the local conditions. The use of appropriate supplements is a
fundamental component of the feeding strategy in order to balance
nutrients at the level of the rumen and of the animal (Preston
and Leng 1987).

The multi-nutritional block (MUB) based on molasses and urea
is being introduced and used in many Asian countries (Leng and
Preston 1983). It is easy to make, of low cost, uses local
resources and is safe to feed.

Acacia mangium, a leguminous tree, has been planted on
thousands of hectares in Vietnam. It produces abundant foliage
especially in the dry season (Ngo and Nguyen 1991).

The aim of this study was to determine:

# The effect on performance of growing crossbred cattle of
using MUB and Acacia mangium leaves as supplements to a
basal diet derived, according to availability, from native
grasses, sugarcane tops, guinea grass silage and rice straw given
adlibitum.

# The effects of the supplements on the rumen ecosystem as
measured by the rates of degradability of standard fibre sources.

Materials and methods

Experiment 1

24 crossbred Holstein-Sindhi heifers (170 kg liveweight, 18-21
months of age) were divided into four treatment groups and fed
the same basal diet (native grasses and molasses given in
restricted amounts; sugarcane tops, guinea grass silage and rice
straw given ad libitum, according to availability). The
experimental period was 90 days in the dry season. The treatments
were:

The Acacia mangium leaves were harvested by hand,
wilted in the shade for 24 hr then chopped into 10-15 cm pieces
before feeding to the animals (NB: Acceptance of the fresh leaves
was low, but improved when the leaves were wilted for 24hr). The
chemical composition (AOAC 1970) of the MUB is shown in Table 1
and of the rest of the feed resources in Table 2. The cattle were
weighed every 14 days and records kept of feed intake.

Experiment 2

A Sindi-local breed (Chinese yellow) heifer of 226 kg
liveweight and 30 months of age was fitted with a rumen cannula.
It was given the following three diets in consecutive periods of
14 days, the measurements of degradability in the rumen of
standard fibre sources being made over the last 2 days of each
period.

The chemical composition of the straw and Acacia leaves is
given in table 3.

Rice straw was used as the test feed to determine the efficacy
of the rumen ecosystem to digest dry matter, organic matter and
fibre. The nylon bag technique described by Orskov et al
(1980) was used. There were four replicates of rice straw during
the incubation for each of the three diets fed to the host
animal.

Table1: Composition
(%) of the MUB used in the two experiments

Ingredients

Exp.1

Exp.2

Urea

10

10

Molasses

35

35

Rice bran

29

-

Peanut husks

-

30

Lime

10

9

Bentonite

10

10

Salt

5

5

Trace
minerals

1

1

Table 2:Checmical composition of feeds used in
experiment 1

% in DM

Feed

DM

N x 6.25

Crude fibre

Sugarcane
tops

39.0

6.99

37.1

Native
grasses

36.1

8.57

37.0

Guinea grass
silage

53.6

4.8

42.5

Rice straw

53.7

5.84

39.9

Molasses

69.3

5.59

0.23

Concentrate

92.0

16.5

12.1

Acacia
foliage

29.7

17.5

44.8

Table 3: Chemical
composition of the feeds used in experiment 2

Feed

DM

% in DM

N x 6.25

Fibre

E Extract

Ash

Rice straw

87.7

4.06

50.1

1.06

10.9

Acacia leaves

30.0

16.7

55.3

5.97

4.82

Results and discussion

Experiment 1

There was an indication that intake of the basal feed (the
low- nutritive value component of the diet) was higher when MUB
was given. Only some 65% of the amounts offered of Acacia
mangium leaves was consumed.

Table 4: Feed
dry matter intakes in experiment 1

C

C+MUB

AM

AMMUB

Feed DM
intake,kg/d

Basal feed

4.19

4.96

4.07

4.63

Total diet

5.08

6.21

5.61

5.49

Table 5: Mean
value for liveweights and gains in experiment 1

C

MUB

Am

AMMUB

SEM(P)

Liveweight(kg)

Initial

169

170

170

169

Final

179

201

186

291

Gain/day*

109

340

185

237

±24(.001)

* Adjusted by covariance for initial weight.

The MUB increased significantly the growth rate when
concentrates were the only supplement, and the combination of MUB
and Acaciamangium was better than that of
concentrates alone or the combination of concentrates and Acacia
mangium. This strongly indicates that (i) there was a
deficiency of rumen ammonia when the basal diet was composed of
grasses, cane tops and rice straw; and (ii) the unsuitability of
the concentrate supplement (90% rice bran and 5% fish meal) for
supplying ammonia for rumen microorganisms. The consistent
positive effect of the MUB supplement on feed intake and on
liveweight gain confirms many reports in the literature which
indicate the value of this type of supplement when the basic diet
is low in nitrogen (Leng and Preston 1984; Preston and Leng 1987;
Sansoucy 1986).

The better results from the combination of MUB and Acacia
mangium leaves than from concentrates justifies the strategy
of supplementing the microbes (with MUB) and the animal (with the
Acacia leaves).

Experiment 2

The rates of degradability of dry matter, organic matter and
crude fibre in the rice straw test feed were increased by
supplementing the rice straw diet of the host animal with MUB.
There was no apparent effect of the Acaciamangium
leaves.

The results with MUB are similar to those reported by Perdok
and Leng (1990). There are data in the literature, for similar
basal diets, indicating beneficial effects on rumen fibre
degradability when supplements of fresh grass (Guttierrez and
Elliott 1981) or leucaena leaves were given. The fact that this
was not observed in experiment 2 may be because of the low rumen
degradability of both the dry matter and the nitrogen in fresh Acacia
mangium leaves (Bui et al 1992).

Conclusion

As a supplement to rice straw for growing heifers, the
combination of MUB and Acacia mangium leaves was better
than that of concentrates or the combination of concentrates and
Acacia mangium. This strongly indicates that (i) there was a
deficiency of rumen ammonia when the basal diet was composed of
grasses, cane tops and rice straw; and (ii) the unsuitability of
the concentrate supplement (90% rice bran and 5% fish meal) for
supplying ammonia for rumen microorganisms.

Acknowledgements

The authors acknowledge the financial support received from
the TCP/FAO project and the SAREC project S/2 Vie 22. They are
also highly appreciative of the co-operation of people of AnPhuoc
state farm, farmers in GoVap district, SongBe Animal Husbandry
Union and students of the Animal Husbandry and Veterinary
Medicine Faculty of UAF.

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